Radio tuning mechanism



y 1943- F. H. DRAKE 2,445,211

RADIO TUNING MECHANISM Filed Jan. 4, 194a Patented July 13, 1948 UNITED STATE PATE :O FICE. I 7 2,445,211" a I nnmo TUNING MECHANISM I .Frederick H. Drake, Boontom llr-l, assignor to Aircraft Radio Corporation, Boonton, N. J., a I corporation of New Jersey Application January 4, 1946, Serial Flo. (j SL129 This invention relates toradiotuning mechanisms and more particularly to knobs: which are secured to shafts for manual rotaton to alter the infective impedance of an adjustable tuning element. I I

Various arrangements have been proposed to obtain a rapid, coarse adjustment of tuning-of a radio receiver'or transmitter or, alternatively; a slow'. .vernier. adjustment of the .tur'iing; An

and usually is, effected by introducing a reduction gear trainibe-tween the manually adjusted shaft and the shaft of the condenser-or other tuning element. 'Such arrangements are quite satisfactory when only small changes are to bev made in the tuning of a circuit, but they are open to the objection that considerable time is lost in tuning from one region to another of a wide range receiver or transmitter. A great number of rotations of the tuning knob are required inview of the reduction gear train, and the resultant slow adjustment of the circuit-tuning is particularly objectionable in the case of radio receivers on military aircraft. Mechanisms for altering the transmission ratio of the gear train have? been proposed but these gear-shift arrangements have been nelatively expensive and not entirely satisfactory in operation.

According'to the present invention, the manually adjustable tuning knob is provided with a disappearing handle or crank arm which is retained in retracted position for fine'tuning and which may be extended to permit high speedoperation of thetuning knob in shifting from one region to another of the tuning range of the apparatus.

An object of the invention is to provide a tuning knob assembly which may be manually notated at low speed or alternatively at high speed. An object is to provide a radio tuning knob having a handle or crank arm which may be telescoped into the knob or, when desired, may be extended into operating position.

These and other objects and the advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a fragmentary side elevation of a tuning system embodying the invention;

Figs. 2 and 3 are front and rear elevations respectively, and on a somewhat larger scale, of the manually operated knob;

Fig. 4 is a view of the novel tuning assembly as seen in axial section; and

Fig. 5 is a similar and fragmentary sectional exceedingly fine adjustment of the tuning'may be, 0

. 5 Claims. (01.745555 view showing the knob with the crank arm in extended position.

In the drawing, the reference numeral I identifies a variable condenser mounted on a chassis 2 and having a shaft 3 in axial alinement with a tuningshaft 6 and secured thereto by a coupling 5. The tuning shaft l is mounted in a plate 6 and extends through the same and through the front panel I of the apparatus. ,An'indicating dial 8 on shaft 4 cooperates with a fiducial mark or pointer, not shown, which is engraved'in or carried by the panel. The shaft 4' is driven by a shaft 9 and gear train ii] which are also mounted on the plate 6, the shaft 9 extending through the panel to receive a knob H.

The elements so far described are typical of the known constructions for obtainingafine or so oalled Vernier adjustment of atuning element of radio, television or other electronicapparatus. Thesensitivity of the adjustment increases with an increase in the step-down transmission ratio of the gear train iii but, unfortunately, any increase the sensitivity of adjustment adds tothe delay incident to a manual operation of the knob i I through many complete revolutions when the apparatus is to be tuned from one-region to another of the-tuning range. Onesuggested compromise between the contradictory design requirements for fine adjustments of the tuning element and for a rapid change fmom one region to another of the tuning range has been to-employ a knob of relatively large size on the shaft}! and a gear train Ii] having a relatively low step-down ratio. 1 Y

According to this invention, the gear train Ill may have a relatively high step-down ratio and the manually operated knob may be of any desired diameter but, preferably, of relatively small diameter, for example of the order of 1%. inches. I'he knob H has 'a rear sleeve 12 in which set screws to are threaded for securing the knob to the gear train shaft 9, and the periphery of the knob may have any desired milledor scalloped form for precluding slipping when the knob is grasped in the usual manner to effect a fine or slow-motion adjustment of the variable impedance I.

A handle or crank is telescoped within the knob l i, the handle being slidably mounted in a socket or cylindrical passagewhich is parallel to and radially spaced from the axis of the knob. The crank comprises a pin I4 having an enlarged head [5 at its forward end, a reduced diameter inner section I6 upon which a bushing I1 is secured by upsetting the end of the pin over the rear face of the bushing, and a sleeve l8 which is rotatable upon the pin I l. The bushing I! has a circumferential groove l9 and the sleeve l8 has a similar circumferential groove 20 for cooperation with a ball 21 and spring 22 which are located in a radial bore in the knob I I to provide an impositive lock for yieldably retaining the handle or crank in extended position as shown in Fig. or in retracted position as shown in'Fig. 4. A stop pin 23 is driven into or otherwise secured in the sleeve section l2 of the knob to limit the inner movement of the handle, thereby to space the inner end of the bushing 11 from the front face of the panel 1 (see Fig. 1) to enable the operator to extend the handle by inserting the tip of a finger between the panel 7 and the bushing IT. The forward end of the handle is substantially flush with the front face of the knob II when the handle is retracted, thereby eliminating the possibility of a mistuning by accidentally striking the handle.

The handle is assembled on the knob II by first inserting the handle assembly from the inner face of the knob, placing the spring 22 and ball 2| in the radial bore, moving the handle assembly forward to retain the ball and spring in their bore, and then inserting the stop pin 23. The inadvertent separation of the handle assembly from the knob is prevented by the stop pin 23 and by a flange 24 at the inner end of the bushing I! which seats against an inner shoulder of the socket when the handle assembly is displaced forwardly into operative position.

The method of operation of the new knob will be apparent from the above description of the construction, The handle is pressed inwardly into retracted position when the effective value of the variable impedance l is to be varied by small increments, and the handle is moved outwardly to serve as a crank arm for the rapid rotation of the knob II when the effective value of the impedance 1 is to be adjusted to another region of its range of values.

While the illustrated construction is the presently preferred embodiment of the invention, it will be apparent that various changes may be made in the design and construction of the telescoping crank assembly of the knob without departure from the spirit and scope of the invention as set forth in the following claims.

I claim:

1. A manually adjustable knob assembly for attachment to a rotatable shaft, said knob assembly comprising a knob and an attached sleeve carrying means for securing the knob to a shaft, said knob having a cylindrical passage therethrough parallel to and radially spaced from the axis of the knob, a handle assembly slidably mounted in said passage, and impositive locking means for yieldingly retaining said handle assembly in retracted position with its forward end substantially flush with the front face of said knob or alternatively in extended position projecting forwardly from the front face of said knob.

2. A manually adjustable knob assembly as recited in claim in combination with means preventing removal of said handle assembly from said knob, said means including a radially extending shoulder within said passage, and a radial flange at the rear of said handle assembly for seating against said shoulder.

3. A manually adjustable knob assembly as recited in claim 1, wherein said handle assembly comprises a pin having a sleeve rotatably mounted thereon.

4,.A manually adjustable knob assembly as recited in claim 1, wherein said knob is provided with a radial bore extending inwardly from the outer edge of the knob to cross and extend beyond said passage, and said impositive locking means comprises a spring-pressed ball within the inner'end of said bore and cooperating grooves in said handle assembly.

5. A manually adjustable knob as recited in claim 1, in combination with stop means on and spaced forwardly of the rear end of the attached sleeve to limit rearward movement of said telescoped handle assembly.

' FREDERICK I-I. DRAKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Publication, Short Wave and Television, Oct. 1937, page 306.

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